According to the prior art, reinforcing shapes with a flattened form used for flexible tubes are, either S-shaped or Z-shaped and are consequently are difficult to manufacture and install precisely and stably in a helical wrap, or are U-shaped as disclosed, for example, in FR 2,561,745. However, flattened U-shaped reinforcing shapes do not have optimum performance with a given layer thickness since the U shape reinforcing element must be thin in order to receive the arms of adjacent windings.